Internal ice deposits have occurred recently on turbofan powered aircraft operating at high altitudes, typically above 30,000 feet and near tropical convective storms. These internal ice deposits have effected engine operation detrimentally: causing loss of engine power and in some cases engine flameouts. The present status of knowledge concerning turbofan engine internal icing is that internal icing is known to occur based on incidents of icing experienced by small aircraft as well as by large passenger jet airliners: incidents that have been experienced and continue to be experienced. However, no understanding of the circumstances or the factors responsible for this type of internal icing is available.
Factors that are different in the new turbofan engine internal icing phenomena compared to engine icing previously encountered are that it is occurring at higher altitudes and in proximity to tropical convective storms. A lack of knowledge regarding the upwelling weather in tropical convective storms is also hindering an understanding of the icing phenomena. A number of theories as to the cause of high altitude turbofan engine internal icing have been offered with some theories lacking a sound basis because they do not take into account engine operation in proximity to a tropical convective storm and other theories suffering from a lack of detailed information about the process.
In 2004, several jet engine shutdowns were experienced on small jet powered aircraft such as the Raytheon's Beechjet aircraft. In this incident, the aircraft had both engines shut down unexpectedly while flying near Jacksonville, Fla. in bad weather at 38,000 feet: the shutdown subsequently believed to be due to internal icing. In 2005, a similar Beechjet aircraft experienced another high altitude shutdown. Additional shutdowns attributed to the new icing phenomena occurred in 2006 with both engines of a Qatar Airways Airbus A330 airliner shut down as the aircraft approached Shanghai airport. Though the engines quickly restarted and a safe landing was accomplished, the shutdown was subsequently attributed to ice deposits inside the jet engines: a situation never before thought possible by the airline industry, aircraft manufacturers and jet engine suppliers.
Reported icing shutdown incidents have continued to this day including the unexpected damage that occurred to three of four engines on an AirBridge Cargo Boeing 747-8F aircraft on Jul. 31, 2013 during cruise at 41,000 feet near Chengdu, China when it was believed to have experienced ice crystal ingestion. In November 2013, Boeing warned airlines about the high altitude icing risk near tropical storms on its new 747-8 and 787 Dreamliner aircraft with high bypass engines made by General Electric, suspected again to be due to ice crystal ingestion. This warning came after six incidents from April to November involving five 747-8s and one 787 in which the aircraft powered by GE's GEnx engines suffered temporary loss of thrust while flying at high altitudes above 30,000 feet. Subsequently, Japan Airlines banned the use of the Dreamliner aircraft in their fleet from flights between Tokyo and Delhi and Singapore as well as on Tokyo to Sydney routes to avoid possible encounters with high altitude tropical storms containing ice crystals.
At the present time, attention is focused on the ingestion of atmospheric ice crystals as the agent responsible for turbofan engine internal icing with several theories offered. It is theorized that some of the ice particles being ingested into the turbofan engine at high altitudes melt and form water due to the increase in inlet air temperature as the air passes into the engine. It is also theorized that additional ice crystals that continually bombard the internal surfaces of the engine lower the surface temperatures to a value that cause the melted water and some of the remaining ice crystals to freeze together on the internal surfaces of the engine. It is also theorized that the ice deposits increase in thickness with time and interfere with the air flow to the engines combustors causing loss of engine power and flameout of the engine. However, experimental measurements supporting these theories are missing,
The upwelling weather near intense tropical storms is not well understood either nor are the effects of the tropical storm understood on how it effects the location and size of ice crystals in the atmosphere thru which the aircraft is passing. The weight of ice crystals and the size of the ice crystals in the atmosphere near tropical storms differ depending on the source of the information studied with various values offered that are in conflict with each other. For instance, NASA Lewis in their wind tunnel icing experiments, to solve the high altitude icing problem, use spray nozzles that produced 5 micron diameter ice crystals though satellite measurements have shown the ice crystals in the upper atmosphere to be larger: in the range from 20 to over 600 microns. Aviation Week and Space Technology magazine also reported that the maximum weight density of ice crystals to be 9 grams per cubic meter while data taken by NASA on recent test flights in tropical zones, still undergoing data reduction and unreported publicly, seem to indicate fewer (lower weight loading) of ice crystals and ice crystals of larger diameter than previously thought. Therefore, in the sample calculation conducted later for the amount of electric power that needs to be provided by the reversed permanent magnet electric generator (reversed PMEG) of the present invention for deicing, a range of weight loadings for ice crystals between 3 grams per cubic meter and 9 grams per cubic meter, are assumed rather than a single value of 9 grams per cubic meter.
What is known without doubt at this time is that icing occurs within turbofan engines with high bypass ratios operating at high altitudes near tropical storms, that icing is related to the existence of ice crystals that are ingested into the aircraft's engines near these storms, and that as a result of ice crystal ingestion and the deposition of ice crystals within the engine, normal engine operation is interfered with. Ingestion of ice crystals is known to be accompanied by icing of internal engine parts with a majority of that icing occurring on the rotational parts of the turbofan engine including engine spinner, fan blades, low pressure compressor casing and low pressure compressor. What is needed is a means to counteract internal icing on these turbofan engines: the type of engines used now on a majority of commercial and passenger aircraft.
Thus, a heretofore unaddressed need exists in the industry to address the aforementioned deficiencies and inadequacies.